https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package java.util.spi;

import jdk.internal.misc.JavaUtilResourceBundleAccess;
import jdk.internal.misc.SharedSecrets;

import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Locale;
import java.util.PropertyResourceBundle;
import java.util.ResourceBundle;
import static sun.security.util.SecurityConstants.GET_CLASSLOADER_PERMISSION;


AbstractResourceBundleProvider is an abstract class that provides the basic support for a provider implementation class for ResourceBundleProvider. 

Resource bundles can be packaged in one or more
named modules, service provider modules.  The consumer of the resource bundle is the one calling ResourceBundle.getBundle(String). In order for the consumer module to load a resource bundle "com.example.app.MyResources" provided by another module, it will use the service loader mechanism. A service interface named "com.example.app.spi.MyResourcesProvider" must be defined and a service provider module will provide an implementation class of "com.example.app.spi.MyResourcesProvider" as follows: 
import com.example.app.spi.MyResourcesProvider;
class MyResourcesProviderImpl extends AbstractResourceBundleProvider
    implements MyResourcesProvider
{
    public MyResourcesProviderImpl() {
        super("java.properties");
    }
    // this provider maps the resource bundle to per-language package
    protected String toBundleName(String baseName, Locale locale) {
        return "p." + locale.getLanguage() + "." + baseName;
    }
    public ResourceBundle getBundle(String baseName, Locale locale) {
        // this module only provides bundles in French
        if (locale.equals(Locale.FRENCH)) {
             return super.getBundle(baseName, locale);
        }
        // otherwise return null
        return null;
    }
 }
 Refer to ResourceBundleProvider for details. 
See Also:
Since:9
@specJPMS
/**
 * {@code AbstractResourceBundleProvider} is an abstract class that provides
 * the basic support for a provider implementation class for
 * {@link ResourceBundleProvider}.
 *
 * <p>
 * Resource bundles can be packaged in one or more
 * named modules, <em>service provider modules</em>.  The <em>consumer</em> of the
 * resource bundle is the one calling {@link ResourceBundle#getBundle(String)}.
 * In order for the consumer module to load a resource bundle
 * "{@code com.example.app.MyResources}" provided by another module,
 * it will use the {@linkplain java.util.ServiceLoader service loader}
 * mechanism.  A service interface named "{@code com.example.app.spi.MyResourcesProvider}"
 * must be defined and a <em>service provider module</em> will provide an
 * implementation class of "{@code com.example.app.spi.MyResourcesProvider}"
 * as follows:
 *
 * <blockquote><pre>
 * {@code import com.example.app.spi.MyResourcesProvider;
 * class MyResourcesProviderImpl extends AbstractResourceBundleProvider
 *     implements MyResourcesProvider
 * {
 *     public MyResourcesProviderImpl() {
 *         super("java.properties");
 *     }
 *     // this provider maps the resource bundle to per-language package
 *     protected String toBundleName(String baseName, Locale locale) {
 *         return "p." + locale.getLanguage() + "." + baseName;
 *     }
 *
 *     public ResourceBundle getBundle(String baseName, Locale locale) {
 *         // this module only provides bundles in French
 *         if (locale.equals(Locale.FRENCH)) {
 *              return super.getBundle(baseName, locale);
 *         }
 *         // otherwise return null
 *         return null;
 *     }
 * }}</pre></blockquote>
 *
 * Refer to {@link ResourceBundleProvider} for details.
 *
 * @see <a href="../ResourceBundle.html#resource-bundle-modules">
 *      Resource Bundles and Named Modules</a>
 * @since 9
 * @spec JPMS

 */
public abstract class AbstractResourceBundleProvider implements ResourceBundleProvider {
    private static final JavaUtilResourceBundleAccess RB_ACCESS =
        SharedSecrets.getJavaUtilResourceBundleAccess();

    private static final String FORMAT_CLASS = "java.class";
    private static final String FORMAT_PROPERTIES = "java.properties";

    private final String[] formats;

    
Constructs an AbstractResourceBundleProvider with the "java.properties" format. This constructor is equivalent to AbstractResourceBundleProvider("java.properties"). 
/**
     * Constructs an {@code AbstractResourceBundleProvider} with the
     * "java.properties" format. This constructor is equivalent to
     * {@code AbstractResourceBundleProvider("java.properties")}.
     */
    protected AbstractResourceBundleProvider() {
        this(FORMAT_PROPERTIES);
    }

    
Constructs an AbstractResourceBundleProvider with the specified formats. The getBundle(String, Locale) method looks up resource bundles for the given formats. formats must be "java.class" or "java.properties". 
Params:
  • formats – the formats to be used for loading resource bundles
Throws:
/**
     * Constructs an {@code AbstractResourceBundleProvider} with the specified
     * {@code formats}. The {@link #getBundle(String, Locale)} method looks up
     * resource bundles for the given {@code formats}. {@code formats} must
     * be "java.class" or "java.properties".
     *
     * @param formats the formats to be used for loading resource bundles
     * @throws NullPointerException if the given {@code formats} is null
     * @throws IllegalArgumentException if the given {@code formats} is not
     *         "java.class" or "java.properties".
     */
    protected AbstractResourceBundleProvider(String... formats) {
        this.formats = formats.clone();  // defensive copy
        if (this.formats.length == 0) {
            throw new IllegalArgumentException("empty formats");
        }
        for (String f : this.formats) {
            if (!FORMAT_CLASS.equals(f) && !FORMAT_PROPERTIES.equals(f)) {
                throw new IllegalArgumentException(f);
            }
        }
    }

    
Returns the bundle name for the given baseName and 
locale that this provider provides. 
Params:
  • baseName – the base name of the resource bundle, a fully qualified
                class name
  • locale –   the locale for which a resource bundle should be loaded
API Note:
A resource bundle provider may package its resource bundles in the
same package as the base name of the resource bundle if the package
is not split among other named modules.  If there are more than one
bundle providers providing the resource bundle of a given base name,
the resource bundles can be packaged with per-language grouping
or per-region grouping to eliminate the split packages.

For example, if baseName is "p.resources.Bundle" then the resource bundle name of "p.resources.Bundle" of Locale("ja", "", "XX") and Locale("en") could be 
"p.resources.ja.Bundle_ja_ _XX" and "p.resources.Bundle_en" respectively. 
 This method is called from the default implementation of the getBundle(String, Locale) method.
Implementation Note:The default implementation of this method is the same as the implementation of Control.toBundleName(String, Locale).
Returns:the bundle name for the resource bundle
/**
     * Returns the bundle name for the given {@code baseName} and {@code
     * locale} that this provider provides.
     *
     * @apiNote
     * A resource bundle provider may package its resource bundles in the
     * same package as the base name of the resource bundle if the package
     * is not split among other named modules.  If there are more than one
     * bundle providers providing the resource bundle of a given base name,
     * the resource bundles can be packaged with per-language grouping
     * or per-region grouping to eliminate the split packages.
     *
     * <p>For example, if {@code baseName} is {@code "p.resources.Bundle"} then
     * the resource bundle name of {@code "p.resources.Bundle"} of
     * <code style="white-space:nowrap">Locale("ja", "", "XX")</code>
     * and {@code Locale("en")} could be <code style="white-space:nowrap">
     * "p.resources.ja.Bundle_ja_&thinsp;_XX"</code> and
     * {@code "p.resources.Bundle_en"} respectively.
     *
     * <p> This method is called from the default implementation of the
     * {@link #getBundle(String, Locale)} method.
     *
     * @implNote The default implementation of this method is the same as the
     * implementation of
     * {@link java.util.ResourceBundle.Control#toBundleName(String, Locale)}.
     *
     * @param baseName the base name of the resource bundle, a fully qualified
     *                 class name
     * @param locale   the locale for which a resource bundle should be loaded
     * @return the bundle name for the resource bundle
     */
    protected String toBundleName(String baseName, Locale locale) {
        return ResourceBundle.Control.getControl(ResourceBundle.Control.FORMAT_DEFAULT)
            .toBundleName(baseName, locale);
    }

    
Returns a ResourceBundle for the given baseName and locale. 
Params:
  • baseName – the base bundle name of the resource bundle, a fully
                qualified class name.
  • locale – the locale for which the resource bundle should be instantiated
Throws:
Implementation Note: The default implementation of this method calls the toBundleName method to get the bundle name for the baseName and locale and finds the resource bundle of the bundle name local in the module of this provider. It will only search the formats specified when this provider was constructed.
Returns:ResourceBundle of the given baseName and locale, or null if no resource bundle is found
/**
     * Returns a {@code ResourceBundle} for the given {@code baseName} and
     * {@code locale}.
     *
     * @implNote
     * The default implementation of this method calls the
     * {@link #toBundleName(String, Locale) toBundleName} method to get the
     * bundle name for the {@code baseName} and {@code locale} and finds the
     * resource bundle of the bundle name local in the module of this provider.
     * It will only search the formats specified when this provider was
     * constructed.
     *
     * @param baseName the base bundle name of the resource bundle, a fully
     *                 qualified class name.
     * @param locale the locale for which the resource bundle should be instantiated
     * @return {@code ResourceBundle} of the given {@code baseName} and
     *         {@code locale}, or {@code null} if no resource bundle is found
     * @throws NullPointerException if {@code baseName} or {@code locale} is
     *         {@code null}
     * @throws UncheckedIOException if any IO exception occurred during resource
     *         bundle loading
     */
    @Override
    public ResourceBundle getBundle(String baseName, Locale locale) {
        Module module = this.getClass().getModule();
        String bundleName = toBundleName(baseName, locale);
        ResourceBundle bundle = null;

        for (String format : formats) {
            try {
                if (FORMAT_CLASS.equals(format)) {
                    bundle = loadResourceBundle(module, bundleName);
                } else if (FORMAT_PROPERTIES.equals(format)) {
                    bundle = loadPropertyResourceBundle(module, bundleName);
                }
                if (bundle != null) {
                    break;
                }
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }
        return bundle;
    }

    /*
     * Returns the ResourceBundle of .class format if found in the module
     * of this provider.
     */
    private static ResourceBundle loadResourceBundle(Module module, String bundleName)
    {
        PrivilegedAction<Class<?>> pa = () -> Class.forName(module, bundleName);
        Class<?> c = AccessController.doPrivileged(pa, null, GET_CLASSLOADER_PERMISSION);
        if (c != null && ResourceBundle.class.isAssignableFrom(c)) {
            @SuppressWarnings("unchecked")
            Class<ResourceBundle> bundleClass = (Class<ResourceBundle>) c;
            return RB_ACCESS.newResourceBundle(bundleClass);
        }
        return null;
    }

    /*
     * Returns the ResourceBundle of .property format if found in the module
     * of this provider.
     */
    private static ResourceBundle loadPropertyResourceBundle(Module module,
                                                             String bundleName)
        throws IOException
    {
        String resourceName = toResourceName(bundleName, "properties");
        if (resourceName == null) {
            return null;
        }

        PrivilegedAction<InputStream> pa = () -> {
            try {
                return module.getResourceAsStream(resourceName);
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        };
        try (InputStream stream = AccessController.doPrivileged(pa)) {
            if (stream != null) {
                return new PropertyResourceBundle(stream);
            } else {
                return null;
            }
        } catch (UncheckedIOException e) {
            throw e.getCause();
        }
    }

    private static String toResourceName(String bundleName, String suffix) {
        if (bundleName.contains("://")) {
            return null;
        }
        StringBuilder sb = new StringBuilder(bundleName.length() + 1 + suffix.length());
        sb.append(bundleName.replace('.', '/')).append('.').append(suffix);
        return sb.toString();
    }

}